Electric valve control circuits



'July 8, 1941. c. c. HERSKIND ELECTRIC VALVE CONTROL CIRCUITS Filed March 30, 1940 2 Sheets-Sheet 1 Fi$.2a.

OUTPUT VOLTAGE OF TRANSFORMER I2 VOLTAGE IMPRESSED ACROSS CONTROL a m mm Inventor Carl C. Herskind M v His Attorney.

July 8, 19 41. c.-c. HERSKIND ELECTRIC VALVE CONTROL CIRCUITS FiledMarch 30, 1940 2 Sheets-Sheet 2 Inventbr:

m W n x" H /W p .w a/ c y b Patented July 8, 1941 ELECTRIC VALVE CONTROLCIRCUITS Carl C. Herskind, Schenectady, N. Y., assignor to GeneralElectric Company, a corporation of New York Application March 30, 1940,Serial No. 326,924

8 Claims.

My invention relates to electric valve circuits and more particularly tocontrol or excitation circuits for electric valve means of the typeemploying an ionizable medium, such as a gas or a vapor.

It is frequently desirable to utilize electric valve apparatus of thetype having immersion-ignitor control members or make-alive electrodes.Electric valves of this type are disclosed and claimed in United StatesLetters Patent No. 2,669,293, granted February 2, 1937 upon. anapplication of Joseph Slepian et al. In electric valve means of thistype, a control member is associated with a cathode of theself-reconstructing type, such as a mercury pool cathode. The controlmember has an extremity thereof extending into the mercury and isconstructed of a material, such as boron-carbide or silicon-carbide,which has a specific electrical resistivity relatively large comparedwith that of mercury. An arc discharge is established by thetransmission of current of a predetermined value to the control member,resulting in the establishment of a cathode spot which eliectsionization of the mercury vapor and in turn establishes an are dischargebetween the anode and cathode of the electric valve means, therebytransmitting current in the anode-cathode circuit. The cathode spot uponthe surface of the cathode is effected by establishing a predeterminedpotential gradient at the surface of the mercury. In accordance with theteachings of my invention described hereinafter, I provide new andimproved control circuits for electric valveapparatus of the typedescribed above.

It is an object of my invention to provide a new and improved electricvalve translating circult.

It is another object of my invention to provide a new and improvedcircuit for electric valve means. V

It is a further object of my invention to provide new and improvedcontrol circuits or excitation circuits for electric valve apparatus,using immersion-ignitor control members, in which means is provided forcontinuously producing a periodic voltage for energizing the controlmembers irrespective of the state of ionization of the medium, and inwhich current is transferred from the control members each cycle uponthe initiation of an arc discharge within the electric valve means.

Briefly stated, in the illustrated embodiments of my invention I providecontrol circuits for electric valves of the type employingimmersionignitor control members in which energizing current istransmitted to the control members periodically to render the electricvalve means conductive periodically. The electric valve means is alsoprovided with an auxiliary electrode, such as auxiliary anode or baffle,which is connected to the excitation circuit to effect transfer ofexcitation current from the control member to the auxiliary electrodeeach cycle upon the establishment of an arc discharge within theelectric valve means, thereby reducing the duty imposed upon the,immersion-ignitor control member.

For a better understanding of my invention, reference may be had to thefollowing description taken in connection with the accompanyingdrawings, and its scope will be pointed out in the appended claims. Fig.1 diagrammatically illustrates an embodiment of my invention as appliedto a bi-phase rectifier for, energizing a direct current load circuitfrom an alternating current supply circuit, and Figs. 2a and 2brepresent certain operating characteristics of the arrangement shown inFig. 1. Fig. 3-diagrammatically illustrates a modification of myinvention as applied to a polyphase'rectifier system. Fig. 3a representscertain operating characteristics of the arrangement shown in Fig. 3.

In Fig. l of the drawings, I have diagrammatically illustrated myinvention as applied to an electric valve converting system forenergizing a load circuit, such as a direct current load circuit I, froma polyphase alternating current supply circuit 2 through electrictranslating apparatus comprising a transformer 3 and electric valvemeans 4 and 5. The electric valve means 4 and 5 are preferably of thetype employing an ionizable medium, such as a gas or a vapor, and eachcomprises an anode 6, a selfreconstructing cathode such as a mercurypool cathode 1, and a make-alive or immersion-ignitor control member 8,preferably constructed of a material having an electrical resistivitylarge as compared with that of the mercury pool cathode l. Theimmersion-ignitor control members 8 may be constructed of boron-carbideor silicon-carbide or other suitable material.

Electric valve means 4 and 5 are provided with auxiliary electrodes 9and 10, respectively. In electric valve means 4 the auxiliary electrode9 is represented as being of the baffle type interposed between theanode t and the cathode l and has several functions. One of thesefunctions is to effect transfer of excitation current from the controlmember 8 to itself upon the initiation of an arc discharge within theelectric valve means 4. Another of its functions is the propagation orextension of the are discharge irom the vicinity of the cathode I to theanode 6 upon the proper encrgization of the control member 8.

In electric valve means 5 the auxiliary electrode I is represented ashaving a difierent form, that is of smaller dimensions than the baffle 9of electric valve means 4, and is positioned somewhat nearer the cathode1 One of the principal functions of the auxiliary electrode I0 is toeffect transfer of the excitation current from the control member 8 toitself upon the initiation of an arc discharge Within the electric valvemeans, or to effect transfer of the excitation current to itself uponthe establishment of an arc discharge between the anode 6 and thecathode I.

I provide an excitation circuit I I for supplying energizing or excitingcurrent to the immersion-ignitor control members 8 to render theelectric valve means 4 and conductive periodically. The excitationcircuit II comprises means for continuously producing a periodic voltageto efiect the proper energization of the control members 8, irrespectiveof the state of ionization of the mercury vapor of the electric valvemeans 4 and 5. This energizing means may comprise a transformer I2energized from a suitable source of alternating current correlated inphase and frequency with respect to the voltage of circuit 2. In thearrangement of Fig. 1, this source of current is derived from thealternating current circuit 2 through a suitable phase shifting means,such as a rotary phase shifting device I3. Transformer I2 is preferablyof the type designed to furnish a periodic voltage of peaked wave form.The transformer I 2 may be arranged to operate on the saturationprinciple, such as that disclosed and claimed in United States LettersPatent No. 2,080,250, granted May 11, 1937 upon an application ofBurnice D. Bedford, and which is assigned to the assignee of the presentapplication.

The excitation circuit II which energizes control members 8 of electricvalve means 4 and 5 also includes unidirectional conducting devices,such as electric discharge devices I4 and I5, so that onlyunidirectional currents are transmitted to the control members 8.Electric discharge devices I4 and I5 are also preferably of the typeemploying an ionizable medium, such as a gas or a vapor, and eachcomprises an anode I6 and a cathode I'I. These discharge devices mayalso include a grid I8 which may be connected to thecathode I I. Thecathode heating elements may be energized from suitable transformers I9energized from a suitable source of alternating current. Currentlimiting resistances and ZI are connected in series relation with theanode-cathode circuits of electric discharge devices M'and I5 andcontrol members I3 of electric valve means 4 and 5, respectively.

As a means for eifecting transfer of excitation current from the controlmembers 8 to the auxiliary electrodes 9 and I 0 upon the initiation ofarc discharges within the electric valve means 4 and 5, I providesuitable connections 22 and 23. These connections are preferablyinterposed between the anodes I6 of electric discharge devices I4 and I5and auxiliary electrodes 9 and I 0 of electric valve means 4 and 5,respectively.

The operation of the embodiment of my invention shown in Fig. 1 will beexplained by considering the system when it is operating as a bi-phaserectifier to transmit unidirectional current to the load circuit I fromthe alternating current circuit 2. In general terms, the electric valvemeans 4 and 5 conduct current alternately to supply the unidirectionalcurrent to the load circuit I. The magnitude of the voltage impressedacross the load circuit depends upon the phase relation of the times ofinitiation of the arc discharges relative to the applied anode-cathodevoltages of the electric valve means 4 and 5. As the times of initiationof the arc discharges are advanced toward the zero point of the positivehalf cycle of applied anodecathode voltage, the magnitude of the directcurrent voltage is increased and, conversely, as the times of initiationof the arc discharges are retarded in time, the direct current voltageis decreased.

The excitation circuit II, and in particular the transformer I2,continuously produce periodic voltages of peaked wave form forenergizing the control members 8 of electric valve means 4 and 5. Thephase of the peaks of voltage of transformer I2, of course, may beadjusted by means of the rotary phase shifting device I3, and hence themagnitude of the output voltage impressed on direct current circuit Imay be controlled thereby. The transformer I2 continuously produces thevoltage of peaked wave form, irrespective of the state of ionization ofthe mercury vapor of the electric valve means 4 and 5, thereby assuringat all times a source of voltage for efiecting the desired energizationof the control members 8. Of course, unidirectional currents aretransmitted to the control members 8 by virtue of the operation of theelectric discharge devices It and I5. During each cycle, as soon as thecurrent transmitted by the electric discharge devices I4 and I5 attainsthe value sufiicient to establish are discharges within the electricvalve means I and 5, the exciting currents are transferred from thecontrol members to the auxiliary electrodes 9 and I0, respectively,thereby reducing the current transmitting duty imposed upon the controlmembers 8. This current transfer is effected by virtue of the lowerimpedance to the flow of current offered by the circuits for theauxiliary electrodes 9 and II! as compared with that of the circuits fortransmitting current to the control members 8.

The above operation may be more fully explained by referring .to theoperating character istics shown in Fig. 2a. Referring particularly tothe operation of the electric valve means 4 including the auxiliaryelectrode 9 in the form of a baffle, curve A represents the open-circuitvoltage of peak-ed wave form supplied by the transformer I2 inexcitation circuit II. This Voltage attains the maximum value c. Theoperating characteristics of curve B show the output voltage of thetransformer I2 in dotted form. The shaded portion of curve B representsthe Voltage applied to the immersion-'ignitor control member 8. At timea the voltage applied to the control member 8 and hence the currenttransmitted. thereto is not sufiicient to effect the establishment of anarc discharge. As the voltage and current increase, at time b, thecurrent has attained a value sufficient to establish an arc dischargeand the current is thereupon transferred to the auxiliary electrode orbafiie 9, thereby reducing the current-carrying duty imposed on thecontrol member 8. The larger portion of the exciting current istransferred to the bafiie 9 which not only maintains the arc dischargeWithin the electric valve means 4 after initiation, but also assists inthe extension of the arc discharge to the anode 6. Curve represents therelative magnitudes of the currents conducted by the control member 8and the baffie 9. In curve C of Fig. 2a the current i represents themagnitude of the current conducted by the control member 8 and irepresents the current conducted by the baffle 9. An inspection of thesecurves reveals that maintenance of the arc discharge within the electricvalve means a is assured by the baffle 9 which transmits a substantialarc-maintaining and arc-propagation current, whereas the amount ofcurrent which the immersi-on-ignitor control member Bis required totransmit is relatively small. This current transfer takes place everycycle upon initiation of the arc-discharge.

The manner in which the auxiliary electrode iii of electric valve means4 operates to relieve the current transmitting duty on control member 8may be explained by referring to the operating characteristics shown inFig. 2b. The dotted curve thereof represents the voltage produced bytransformer I 2 and the heavy curve D represents the voltage impressedacross and hence the current transmitted by the immersion-ignitorcontrol member 8. As soon as the arc discharge is established betweenthe anode 6 and the oathode l, the auxiliary electrode Ill transfers thecurrent to itself, reducing the current through the control member 8.

In Fig. 3 I have diagrammatically illustrated another embodiment of myinvention as applied to a polyphase electric valve converting systemwhere only the control and excitation circuits are shown. With theexception of the main or power transmitting electric valves 2435, theassociated power transmitting apparatus are not illustrated. It isbelieved that the connections of the associated power circuits will beapparent to those skilled in the art. Electric valve means 2435 arerepresented as being of the same type as electric valve means in Fig. 1and each comprises an anode 36, a mercury pool cathode 31, animmersion-ignitor control member 38 and an auxiliary electrode 39.

Suitable sources of periodic voltage for energizing the control members38 are provided by an inductive network, such as a plurality oftransformers 40 and 4| including primary windings 42, 43 and secondarywindings M, 45, respectively. The voltages furnished by. windings Ml and45 may be either sinu-soidal or of peaked wave form. A suitable phaseshifting means, such as an auto-transformer 46, may be interposedbetween the alternating current supply circuit 2 and the transformersIll] and ll to afford any desired phase shift in the control voltages.The transforming means 49 and ll, of course, may be of the type designedto produce voltages of peaked wave form. interposed between thetransformers 49 and 4!, which constitute excitation circuits for thecontrol members 38 of electric valve means 2435, I provide a pluralityof electric discharge devices 41-58 which serve to transmit onlyunidirectional currents to the control members 38 and which are also ofthe controlled type, thereby providing a means for initiating theenergization of the control members 38 at predetermined times duringeach cycle of the periodic voltages supplied by secondary windings 49and 45. The control electric discharge devices 41-58 are preferably ofthe type employing an ionizable medium and each comprises a controlmember or grid 59, the conductivity of which is controlled by means of aplurality of control circuits to be described immediately hereinafter.

Periodic voltages for the control of the conductivity of the electricdischarge devices -58 may be obtained by means of suitable control orexcitation circuits comprising a plurality of transformers 6E and BIincluding primarywindlugs 62 and 63, and secondary windings 64 and 85,respectively. In the arrangement of Fig. 3,

l8 secondary windings 64 and B5 of transformers 60 and GI are shown aseach being connected through a pair of conductors to the oathode and thegrid of the respective electric discharge devices ll58. It will beunderstood that the groups of secondary windings 64 and 55 may bearranged to have neutral connections which are connected to the commonconnection for cathodes 3! of electric valve means 2l35. Currentlimiting resistances 66 and 67 may be connected in series relation withthe grids 59 to protect the input circuits to the electric dischargedevices 67-59. The phase of the periodic voltages impressed on the grids59 of electric discharge devices l'i--58 may be controlled or adjustedby means of any suitable arrangement, such as a rotary phase shifter 68connected between the transformers 69 and SI and the alternating currentsupply circuit 2.

The embodiment of my invention shown in Fig. 3 operates in substantiallythe same way as that explained above in connection with the arrangementof Fig. 1. 'Ihe electric valves 24-45 are rendered conductive in apredetermined order or sequence by the proper energization of theassociated control members 38. Unidirectional currents are transmittedto the control members 38 from. the excitation circuits, comprisingtransformers 4E! and ti, through the control electric d scharge devicestl58. The discharge devices 4'l-58 are preferably rendered conductive ata time when the excitation current is sufficient to establish an arcdischarge within the associated main or power electric valve means24--35. In this manner, the average current which the control members 38is required to transmit is still further reduced. As soon as the arcdischarge is established within the electric valve means 24-35, thecurrent is transferred to the auxiliary electrodes 39 which maintain theare discharges. The magnitude of the output voltage, and hence the poweroutput of the electric valve means 24-35, is controlled by means of therotary phase shifter 5.3 which determines the time during the cycle ofvoltage of circuit 2 at which the respective electric valve means arerendered conductive.

Curve E of 3a represents the voltage supplied by one of the windings 44and 45, as for example windin Mi associated with electric dischargedevice l'i and electric valve means 24. Curve F represen s the voltageand the current supplied to control member 38 of electric valve means24. At time 1 the grid voltage furnished by secondary winding 84 oftransformer 60 is proper to render electric discharge device 41conducting. Current'is thereupon conducted to control member 38 fromwinding 44 through electric discharge device 4?. At time 5/ an arcdischarge is established within electric valve means 24 and theexcitation current. or the principal part of it, is transferred to theauxiliary anode 39. It

will be understood that the current which control member 38 is requiredto conduct is there fore maintained at a small value without sacrificingprecision of control.

While I have shown and described my invention as applied to particularsystems of connections and as embodying various devices diagrammaticallyshown, it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention, and I,therefore, aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, electric valve means of the type employing anionizable medium capable of supporting an arc discharge and comprisingan anode, a cathode, an immersion-ignitor control member and anauxiliary electrode, an excitation circuit comprising a saturableinductive device for continuously producing a periodic voltage forefiecting energization of said control member, a unidirectionalconducting device connected in said excitation circuit for transmittingonly unidirectional impulses of current to said control member, andmeans exclusive of said unidirectional conducting device and connectedbetween said saturable inductive device and said auxiliary electrode foreffecting transfer of current from said control member to said auxiliaryelectrode during each cycle of the voltage of said alternating currentcircuit upon initiation of an are discharge vvithin said electric valvemeans.

2. In combination, an alternating current cir cuit, a direct currentcircuit, electric translating apparatus connected between said circuitsand including electric valve means of the type employing an ionizablemedium capable of supporting an arc discharge and comprising an anode, acathode, an immersion-ignitor control member and an auxiliary electrode,an excitation circuit comprising a winding for continuously producing aperiodic voltage to energize said control member during each cycle ofvoltage of said alternating current circuit, a unidirectional conductingdevice connected between said control member and said winding totransmit only unidirectional impulses of current to said control member,and means exclusive of said unidirectional conducting device forconnecting said auxiliary electrode to said winding to effect thetransfer of excitation current from said control member to saidauxiliary electrode during each cycle of voltage of said alternatingcurrent circuit upon the initiation of the arc discharge occasioned bythe transfer of current through said control member.

3. In combination, an alternating current circuit, a direct currentcircuit, electric translating apparatus connected between said circuitsand including electric valve means of the type employing an ionizablemedium capable of supporting an arc discharge and comprising an anode, acathode, an immersion-ignitor control member and an auxiliary electrode,excitation means energized from said alternating current circuit forcontinuously producing a periodic voltage for energizing said controlmember to render said electric valve means conductive at a predeterminedtime during each cycle of voltage of said alternating current circuit, aunidirectional conducting device connected between said excitation meansand said control member to transmit unidirectional current to saidcontrol member, means exclusive of said unidirectional conducting deviceand connected between said excitation means and said auxiliary electrodeto permit transfer of current from said control member to said electrodeupon the initiation of an arc discharge (between said anode and saidcathode occasioned by the energization of said control member, and meansfor controlling the time of energization of said control member by saidexcitation circuit relative to the voltage of said alternating currentcircuit.

4. In combination, an alternating current circuit, a direct currentcircuit, electric translating apparatus connected between said circuitsand including electric valve means of the type employing an ionizablemedium capable of supporting an arc discharge and comprising an anode, acathode, an immersion-ignitor control member and an auxiliary electrode,excitation means comprising means for continuously producing a periodicvoltage to energize said control member irrespective of the state ofionization of said medium, a control electric discharge device connectedbetween said excitation means and said control member and comprising ananode and a cathode, and means connected between said electrode and theanode of said control discharge device to permit transfer of currentfrom said control member to said auxiliary electrode during each cycleof the voltage of said alternating current circuit upon the initiationof an arc discharge within said electric valve means occasioned by theenergization of said control member.

5. In combination, an alternating current circuit, a direct currentcircuit, electric translating apparatus connected between said circuitsand including electric valve means of the type employing an ionizablemedium capable of supporting an arc discharge and comprising an anode, acathode, an immersion-ignitor control member and a baflle interposedbetween said cathode and said anode, said bafile being arranged tooperate as an exciting anode and to assist in the extension of the arcdischarge from said cathode to said anode upon the energization of saidcontrol member, excitation means comprising means for continuouslyproducing a periodic voltage to energize said control member to rendersaid electric valve means conductive during each cycle of voltage ofsaid alternating current circuit, a control electric discharge deviceconnected between said excitation means and said control member andincluding an anode and a cathode, and means connected between saidbaffie and the anode of said discharge device to permit transfer of thecurrent from said control member to said bafile during each cycle of thevoltage of said alternating current circuit upon the initiation of anarc discharge within said electric valve means.

6. In combination, an alternating current circuit, a direct currentcircuit, electric translating apparatus connected between said circuitsand including electric valve means of the type employing an ionizablemedium capable of supporting an arc discharge and comprising an anode, acathode, an immersion-ignitor control member and an auxiliary electrode,excitation means comprising means for continuously producing a periodicvoltage to render said electric valve means conductive periodically, anelectric discharge device of the controlled type having a grid and beingconnected between said excitation means and said control member, meansfor energizing said grid to render said electric valve means conductive,and means exclusive of said electric discharge device and connectedbetween said excitation means and said auxiliary electrode to permittransfer of current from said control member to said auxiliary electrodeduring each cycle of the voltage of said alternating current circuitupon the initiation of an arc discharge within said electric valvemeans.

7. In combination, an alternating current circuit, a direct currentcircuit, electric translating apparatus connected between said circuitsand including electric valve means of the type employing an ionizablemedium capable of supporting an arc discharge and comprising an anode, acathode, an immersion-ignitor control member and an auxiliary electrode,excitation means comprising means for continuously producing a periodicvoltage to render said electric valve means conductive periodically, anelectric discharge device connected between said excitation means andsaid control member and comprising a grid for initiating energization ofsaid control member through said discharge device, means for impressingon said grid a variable control voltage to determine the time duringeach cycle of voltage of said alternating current circuit at Which saidelectric discharge device is rendered conducting, and means exclusive ofsaid electric discharge device and connected between said excitationmeans and said auxiliary electrode to permit transfer of current fromsaid control member to said auxiliary electrode during each cycle of thevoltage of said alternating current circuit upon the initiation of anarc discharge within said electric valve means.

8. In combination, an alternating current circuit, a direct currentcircuit, electric translating apparatus connected between said circuitsand including a pair of electric valve means each being of the typeemploying an ionizable medium capable of supporting an arc discharge andeach comprising an anode, a cathode, an immersionignitor control memberand an auxiliary electrode, excitation means comprising means energizedby alternating current for continuously producing an alternating voltageof peaked wave form to energize the control members alternately, meansconnected between said excitation means and the control member of eachof said electric valve means and each comprising in series relation aunidirectional conducting device and an impedance element, and meansconnected be tween said excitation means and each of the auxiliaryelectrodes to permit transfer of current from the control member to theassociated electrode during each cycle of voltage of said alternatingcurrent circuit upon initiation of an arc discharge within the electricvalve means occasioned by the energization of the associated controlmember.

CARL C. I-IERSKIND

